The present invention relates to nonferrous extrusion equipment, and more particularly to a control system for coordinating and monitoring the movement of material through such equipment.
A typical nonferrous extrusion line, such as those used in extruding aluminum, typically consists of four processing stations and three transition areas. The processing stations are the furnace/shear station, the press/puller station, the stretcher station, and the saw station. The transition areas are the transveyor/loader area, the cooling table area, and the batching table area. The transition areas separate the processing stations so that material flows through the facility in the following order: furnace or furnace/shear, transveyor/loader, press/puller, cooling table, stretcher, batching table, and saw. In the processing stations, the equipment has contact with the metal and can track the material easily. Tracking is difficult in the transition areas because material is added to and removed from each transition area at different rates.
In the furnace/shear station, billets of raw material are preheated. In a furnace/shear, the billets are also cut to length for extruding. The heated, sized billets are then carried by the transveyor/loader into the extrusion press. The press forces the softened material through an extrusion die to produce an elongated extrusion having a uniform cross-section throughout its length. Because the material exiting the press is not rigid, pullers are used to facilitate transporting the material away from the extrusion press. The pullers draw the material on to a cooling table where the extruded material cools. The extrusions are then stretched to exert a longitudinal force on the extrusions. Due to the structural properties of the metal, stretching straightens and rigidifies the extrusion. The stretched extrusions are then accumulated on a batching table into batches, which are forwarded to the saw for cutting. The processed extrusions are then finished and/or stored for subsequent supply.
The transition areas hold varying amounts of material throughout operation of the system. Each of the furnace/shear, press/puller, and stretcher stations deposits material into the subsequent transition area at a dynamic rate. Similarly, each of the press/puller, stretcher, and saw stations removes material from a transition area at a dynamic rate. For example, one, two, three, four, or even more extrusions can be fabricated simultaneously from a single press cycle depending on the die configuration. Similarly, the stretcher and saw may operate on only a single extrusion at a time or up to four or more extrusions at a time.
As can be readily appreciated, the amount of material in the transition areas varies dynamically with the operation of the system. Since different "jobs" for different pieces are run sequentially through the system, a "steady state" of material flow through the transition areas is the exception rather than the rule.
Prior computer control for extrusion operations are unsophisticated by today's standards. Typically, a programmable logic controller (PLC) is provided in conjunction with each processing station. A first PLC is provided for the furnace/ shear, a second for the press/puller, and a third for the stretcher and saw. The PLC's are each operated by human operators, who observe conditions at their individual stations and input commands into the PLC to control the equipment. Papers must be transported throughout the extrusion facility to inform the operators of the approaching jobs. Such a "paper trail" passes from operator to operator as the extrusion passed through the system. The operator must then recognize the material within the transition area approaching his station and take the appropriate action to properly process the material. Obviously, even the smallest of manufacturing mistakes can result in substantial losses of entire jobs or batches of material. These problems are further complicated when different jobs or orders share the same extrusion cross-section and length. In such case, the only way to determine the division between the orders is to maintain a physical count of the extrusions in each transition area.